In 19th century Japan, rice seedlings suffered an affliction that made them grow taller than other plants--so tall they could not support their own growth, and they collapsed and then died. This "foolish seedling disease" was caused by a chemical secreted by the fungus Gibberella fujikuroi. The chemical turned out to be a ubiquitous plant hormone, one that stimulates plant cells to elongate and divide. Used in various strengths at various times as a plant develops, this gibberellic acid induces a range of effects, sometimes helpful, sometimes unintended and sometimes undesirable. Using gibberellic acid can be tricky.
Gibberellic acid is used to help seeds germinate and germinate more quickly. Seeds that are difficult---those that need notching and soaking---germinate more readily, old seeds show a higher germination rate and dormant seeds will break their sleep when the acid is applied. Tubers, too, awaken, sprouting sooner than normal.
Gibberellic acid is used to promote root formation, though it can have the opposite effect or even no effect at all. The differences depend on light and the concentration of gibberellic acid applied, experiments in Denmark showed.
Under the influence of gibberellic acid, flowers can do some unexpected things. The hormones can be used to effect the sex of the flowers, suppress flowers and, if the plant has developed enough, can make plants burst into bloom early. If frost has struck blossoms, spraying them with gibberellic acid when they first start to wither might bring some back.
Plant clones that can't normally reproduce among themselves can succeed at pollination with an application of both gibberellic acid and another plant hormone called cytokinin. Gibberellic acid can also be used to create hybrids by pollinating two closely related species by hand and applying the acid to the flowers.
Fruit size can be increased on some fruiting plants if they are sprayed when the fruits first set. This is commonly practiced on grape plants, and not only can some grapes grow larger, they elongate. Also, fruiting plants in general produce a better crop when fruit is thinned. Spraying gibberellic acid when blooms appear can accomplish this.
More fruit sets successfully when gibberellic acid is applied, increasing yield. Even when pollination is incomplete, the fruits will grow. Given the incomplete pollination, such products will largely be seedless. Gibberellic acid also spurs fruit to grow more rapidly and fruits mature faster.
As an agent of elongation and division, gibberellic acid can be used to cause trees to grow throughout their growing season. The hormone is applied around the terminal buds of trees. These are found at the end of stems instead of at the sides.